germination of rice can be enhanced significantly when inoculated with
Herbaspirillum (Pereira et al. 1988).
20.3.3.10 Rhizobium
Rice roots can be colonized endophytically with Rhizobium leguminosarum
bv. trifolii in fields where rice crop is rotated with Egyptian berseem clover (Trifolium alexandrinum), substituting 25–33% of the amount of N-fertilizer
recommended for rice in field (Yanni et al. 1997). Field trials showed that rice
yield increased with the inoculation of this bacterium by 3.8 t ha
À1 (Yanni et al.
2001). This bacterium is also able to colonize endophytically inside rice roots grown
under gnotobiotic conditions. Grain yield and agronomic N-fertilizer efficiency was
significant including shoot and root growth promotion. However, the population size
was not higher showing the low numbers of the order of 10
5 cells (colony-forming
units) per gram dry weight, too low for significant BNF.
Laboratory and greenhouse studies conducted at the International Rice Research
Institute (IRRI) showed that when rice is inoculated with this strain the expression
levels of both the growth and yield reporter genes (e.g. lacZ or gusA) connected to
rhizosphere associations improve. Other diazotrophs including Azospirillum,
Herbaspirillum, and Burkholderia are closely associated with the rhizosphere of
rice plants (Baldani et al. 2000; Balandreau 2002; Malik et al. 2002). All these
diazotrophs can provide urea-N by BNF as supplementary amount to the crops but
only in the right condition for expression of N 2 -fixing activity and subsequent
transfer of N to plants (Kennedy et al. 2004). Watanabe et al. (1987), and Roger
and Ladha (1992) concluded that diazotrophs can supplement 20–25% of the total N
needs of rice, considering all the results of many works conducted at IRRI at Los
Baños in the Philippines.
20.3.3.11 Bacillus
Bacillus subtilis is a gram-positive bacterium, rod-shaped, and catalase-positive, and
belongs to phylum Firmicutes, class Bacilli, order Bacillales, Family Bacillaceae
(Turnbull, 1996). The B. subtilis strain CB-R05 was isolated and studied from the
rice plants, and is a diazotrophic endophytic plant growth-promoting bacterium
(Ji et al. 2014a, b). In their studies, a gfp-tagged B. subtilis CB-R05 was transformed
by electroporation, and then rice seedlings were inoculated with the gfp-tagged
CB-R05 bacteria. Localization and colonization of the gfp-tagged CB-R05 bacteria
was confirmed on the tips and xylems of rice roots in a hydroponic culture and soil
culture system using confocal laser scanning microscopy (CLSM) until the 16 days
after inoculation during experiments (Ji et al. 2014b).
412
S.-C. Chun
Herbaspirillum (Pereira et al. 1988).
20.3.3.10 Rhizobium
Rice roots can be colonized endophytically with Rhizobium leguminosarum
bv. trifolii in fields where rice crop is rotated with Egyptian berseem clover (Trifolium alexandrinum), substituting 25–33% of the amount of N-fertilizer
recommended for rice in field (Yanni et al. 1997). Field trials showed that rice
yield increased with the inoculation of this bacterium by 3.8 t ha
À1 (Yanni et al.
2001). This bacterium is also able to colonize endophytically inside rice roots grown
under gnotobiotic conditions. Grain yield and agronomic N-fertilizer efficiency was
significant including shoot and root growth promotion. However, the population size
was not higher showing the low numbers of the order of 10
5 cells (colony-forming
units) per gram dry weight, too low for significant BNF.
Laboratory and greenhouse studies conducted at the International Rice Research
Institute (IRRI) showed that when rice is inoculated with this strain the expression
levels of both the growth and yield reporter genes (e.g. lacZ or gusA) connected to
rhizosphere associations improve. Other diazotrophs including Azospirillum,
Herbaspirillum, and Burkholderia are closely associated with the rhizosphere of
rice plants (Baldani et al. 2000; Balandreau 2002; Malik et al. 2002). All these
diazotrophs can provide urea-N by BNF as supplementary amount to the crops but
only in the right condition for expression of N 2 -fixing activity and subsequent
transfer of N to plants (Kennedy et al. 2004). Watanabe et al. (1987), and Roger
and Ladha (1992) concluded that diazotrophs can supplement 20–25% of the total N
needs of rice, considering all the results of many works conducted at IRRI at Los
Baños in the Philippines.
20.3.3.11 Bacillus
Bacillus subtilis is a gram-positive bacterium, rod-shaped, and catalase-positive, and
belongs to phylum Firmicutes, class Bacilli, order Bacillales, Family Bacillaceae
(Turnbull, 1996). The B. subtilis strain CB-R05 was isolated and studied from the
rice plants, and is a diazotrophic endophytic plant growth-promoting bacterium
(Ji et al. 2014a, b). In their studies, a gfp-tagged B. subtilis CB-R05 was transformed
by electroporation, and then rice seedlings were inoculated with the gfp-tagged
CB-R05 bacteria. Localization and colonization of the gfp-tagged CB-R05 bacteria
was confirmed on the tips and xylems of rice roots in a hydroponic culture and soil
culture system using confocal laser scanning microscopy (CLSM) until the 16 days
after inoculation during experiments (Ji et al. 2014b).
412
S.-C. Chun